Vehicle heaters may be designed as auxiliary or parking heaters. Auxiliary heaters require a running vehicle engine for their operation. In contrast, parking heaters are designed, in general, for an engine-independent operation. In addition, parking heaters may, of course, also be operated in an auxiliary function in addition to their parking heater function.
Some modern vehicle engines have such a high efficiency that in cool weather, they are not always able to make available a sufficient amount of waste heat for heating the interior space of the vehicle. This problem arises, e.g., especially in the case of direct-injection diesel engines with low fuel consumption. In cases of engine waste heat which is too low for the sufficient heating of the interior space of the vehicle, the engines or vehicles are provided with auxiliary heaters. These auxiliary heaters are usually burner-operated and heat the cooling water of the engine, which is used for heating the vehicle via a heat exchanger present in the auxiliary heater. The heat exchanger is an integrated part of the cooling water line or at least of a partial cooling water circuit supplying the vehicle heater. If the cooling water temperature is too low for sufficiently heating the interior space of the vehicle, the burner of the auxiliary heater can be switched on automatically when the engine is running in order to sufficiently heat the cooling water. A control device ensures that the auxiliary heater operates only when the cooling water temperature is too low in relation to the outside temperature and a desired heat demand for heating the interior space of the vehicle. In contrast, the auxiliary heater remains inactive in all other cases. For reasons of efficiency and costs, such auxiliary heaters are provided only with the functional parts that are absolutely necessary for their function as auxiliary heaters. Therefore, these devices have, in particular, no cooling water-circulating pump of their own, i.e., the cooling water circulation is generated exclusively by the cooling water-circulating pump of the vehicle engine. The cooling water pump of the engine, which must be present for cooling the engine with cooling water, on the one hand, and for supplying the engine-dependent, usual vehicle heater, on the other hand, even without an additional vehicle heater, is mechanically driven by the engine at least during the drive mode of the engine. An electric circulating pump is also additionally provided in some cases in order to ensure a large throughput corresponding to the cooling demand of the engine and to the heat demand of the heater even during the idling of the engine, in particular, when its speed is sometimes too low for a sufficient capacity of the pump.